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[John Anderson]

We have a screen flicker from our video presentation hardware, which I have identified the cause as a new hearing aid loop amplifier. (It appeared when we introduced a new H.A.L. system, & disappears when I turn the amp off). Obviously thats the cause, but how do I rectify/solve the problem? Any ideas please ?

[Christopher Buehring]

How close to the "video presentation hardware"(projector?) is the amplifier?

Are the two pieces of equipment on the same electrical circuit?

Are the two connected in any way by an audio chain...perhaps your video computer is also hooked to your sound system?

[John Anderson]

1. We have a raised platform at the back of the hall for Sound, Lighting, & Video, & also contains The Hearing Aid Amp. The projector is mounted from the ceiling, some 40 feet away (in a direct line)
2. Not sure if they are on the same circuit - I will check this.
3. Yes the video computer does have an audio out going to the main PA desk. I will try some trouble shooting here by removing this connection.

Thanks for these tips.

[Tim Urner]

We had a flicker once that was a ground loop manifesting itself in a inaudible way.

Sounds like a little voodoo.

Make sure the entire system, and everything that plugs into it comes off of the same AC panel.

[Brad Weber]

Is should be fairly easy to temporarily get the ALS loop amp in the same power as the projector and sources using extension cords.  But it could also by from the actual loop itself.

Someone please correct me if this makes no sense, but what happens if you disconnect the HAL input from the house audio system and provide it an isolated source (a battery powered CD player or something like that would be ideal)?  At that point there should be no physical coupling through the cabling paths.  If you still get the flicker then you might want to look at where the video cable runs in relation to the HAL antenna, especially if they are not in separate conduit runs.

[Dan Nelson]

So we have identified 3 possible causes?  


1. RF from the HAL
2. Lack of good ground due to separate AC CKTS
3. A ground loop made up of AC and Audio.


I would suggest trying to eliminate these one at a time. Finding the cause may be the hard part. The correction may be easy.  

Oh, Quick question. Is the flicker sporatic or is it consistent?  Is there a patern or does it seem random?

[John Anderson]

The flicker is 'flickering' in time to the music. It also occurs when playing a CD, which is directly connected to the PA desk!
I have also sourced an electrician within the church who is going to help me connect to different phases of the 3 phase power source. (I am in Australia, with different power specs, so hope this makes sense)

[Brad Weber]

If the flicker is in time to the audio then it is likely an RF issue.  Does your video system have any other outputs or a preview capability?  If so, do you see the flicker in those signals or only the projector?  Is the video run to the projector in metal conduit?  Do you know if the video cabling runs next to or crosses the HAL loop antenna?

On the HAL side, is the HAL transmitter physically close to any of the video equipment?  Have you discussed this problem with the HAL manufacturer?

[ProSoundWeb Community]